7 In. to 4 In. round Reducer Hemmed collar edges for an improved fit and increased strength•Connects 7 in. pipe to 4 in. pipe in duct run•Seal seams with code-approved mastic, sealant or duct tape (sold separately)•Always insulate ductwork for greater system efficiency and comfort (insulation not included)•Don’t know how much to order? A GAF QuickMeasure report provides all of the measurement data you need when planning your material orders. A complete bill of materials, with Home Depot product SKUs, is provided with each single-family report delivered in under 1 hour. Learn more here. [gaf.com [gaf.com]]•Return Policy